All of the foregoing applications are herein incorporated by reference.
1. Field of the Invention
This invention relates to injection of pressurized materials through a distribution system, such as injection molding of plastic melt in a hot runner injection molding system. More specifically, this invention relates to an improved injection molding system in which the rate of material flow through two or more gates is independently controlled.
2. Description of the Related Art
U.S. Pat. No. 5,556,582 discloses a multi-gate single cavity system in which the rate of melt flow through the individual gates is controlled independently via a control system according to specific target process conditions. This system enables the weld line of the part (the section of the part in which the melt from one gate meets the melt from another gate) to be selectively located. It also enables the shape of the weld line to be altered to form a stronger bond.
The ""582 patent discloses controlling the rate of melt flow with a tapered valve pin at the gate to the mold cavity. It also discloses placing a pressure transducer inside the mold cavity. Placing the pressure transducer inside the mold cavity can result in the pressure transducer sensing pressure spikes which can occur when the valve pin is closed. A pressure spike sensed by the transducer can cause an unintended response from the control system, and result in a less precise control of the melt flow than desired.
The control system disclosed in the ""582 patent uses the variables of valve pin position and cavity pressure to determine what position the valve pin should be in. Thus, the algorithm performed by the control system in the ""582 patent utilizes two variables to control the rate of melt flow into the cavity.
Injection molding apparati, systems and methods are provided for limiting forward valve pin movement during flow control. According to one embodiment, an injection molding apparatus is provided that includes an actuator, and a valve pin coupled to the actuator. The valve pin is adapted to open and close a gate to a mold, and to control a rate of material flow through the gate during an injection cycle. The actuator is further adapted to control the valve pin in a first range of movement in which the valve pin is adapted to control the rate of material flow and cannot close the gate, and to control the valve pin in a second range of movement which includes the valve pin closing the gate.
According to another embodiment an injection molding apparatus is provided that includes an actuator including first and second valves, and a valve pin coupled to the actuator. The valve pin is adapted to open and close a gate to a mold, and to control a rate of material flow through the gate during an injection cycle. The first valve is adapted to control a range of movement of the valve pin, and the second valve is adapted to cause the valve pin to close the gate.